Roller or peristaltic (squeeze) pumps are positive displacement pumps in which the fluid to be conveyed is pressed through a tube by elastic external mechanical deformation of the same. Due to the smooth conveying of the fluid (without shearing or swirling the latter) peristaltic pumps are also used especially for medical purposes.
A flexible/elastically deformable tube is basically inserted in the housing of a generic peristaltic pump so that it is guided around a rotatable pump head over a predetermined peripheral section on which a number of angularly spaced rollers are rotatably supported which upon appropriate rotation of the pump head are sequentially brought into rolling engagement with the tube and compress/squeeze off the same. The tube is supported either on the outside of the pump housing or it is tensioned around and against the pump head at a predetermined tensile force.
In each design the movement of the pump head results in the fact, however, that the respective squeeze-off position of a just engaging roller moves forward along the tube and thereby advances the fluid to be pumped inside the tube portion immediately upstream of the respective roller. The suction vacuum in the tube portion immediately downstream of the respective roller is generated, as a rule, by the inherent elasticity of the tube material by virtue of which the tube attempts to regain its original constructional shape.
Due to the increasingly stricter hygienic regulations as well as more demanding user requests, it has become common practice to design at least those components of a peristaltic pump especially when used in the medical field as one-way articles which get in direct contact with the fluid to be pumped. These include primarily the tube which consequently has to be most easily removable and insertible. For this purpose, a plurality of tube units and tensioning devices are known from the state of the art, some of which shall be mentioned hereinafter:
Basically it is possible to pre-mount both the tube and the pump head in a kind of cartridge as a separate tube unit which during a replacing operation merely has to be inserted/locked in the housing of the peristaltic pump such that the pump head is engaged to co-rotate with a drive shaft of an electric motor or a gear unit connected thereto, for example. Although this solution strongly facilitates the replacing operation and at the same time also ensures high operating reliability, as the cartridge can be designed as a closed housing unit, whereby rotating elements are encased so as to be inaccessible from outside, this constitutes a comparatively expensive design variant.
The pump head is a rather complicated component consisting of a plurality of single parts movable/rotating relative to each other (as indicated already before) which actually would not have to be replaced, because it is not directly contaminated by the fluid to be pumped. Therefore it is by far less expensive to provide merely the tube as one-way article. For exchanging the latter, however, the tube has to be removed from the pump head and attached thereto again, wherein a pretensioning force has to be overcome by which the tube is tensioned around the pump head. In order to facilitate replacement of merely the tube (with the pump head being retained), therefore a specific tensioning mechanism has been developed by which the tube can be relaxed and tensioned for an exchanging operation.
G 94 11 183 discloses a simple design of such tensioning device. Accordingly, the tube is provided/configured with two axially spaced bead-like stops/holding fixtures, whereas the pump housing is provided inside the tube mounting case formed or inserted therein with a transverse strip or beam as tube mount in which two notches are formed. In order to insert the tube into the tube mount the one beaded stop is locked/hooked into the one notch and subsequently the tube is pulled around the pump head. Finally the other beaded stop is locked/hooked into the other notch. This inserting operation is very time-consuming and complicated as the stops have to be hooked into the notches under tensile stress of the tube, which requires particular skills and force by an operating person.
As an alternative to this, it is also possible to provide a driving beam as tube mount which at its two axial ends is tightly connected to the tube at two axially spaced tube portions so that the tube (central tube portion) forms a loop between the beam ends. The beam and the tube thus constitute a separate replaceable tube unit.
The tube formed in this way is now laid/guided over the pump head with its loop area and the driving beam is locked in a tensioning device. The tensioning device preferably provides a guide rail/groove for the driving beam along which the driving beam is displaced while the loop area is tensioned, until the driving beam engages in a detachable mount/locking inside the tube mounting case. Although this design facilitates the inserting operation of the tube, the tube has to be tensioned in the area of the loop simultaneously at two ends of the loop area and thus at two flanks forming relative to the pump head, which requires a greater effort which cannot be applied by any operating person.
Finally, the exchange of merely the tube (and not the pump head) requires free access from outside even to the rotating components which either remains opened also during operation for reasons of cost or can be at least partly closed by means of an additional service/protective door. The latter does not only render the peristaltic pump more expensive, but also constitutes a source of danger in so far as the door has to be closed in an additional step, which might be forgotten.